A typical lock comprises a locking member, such as a lock bolt or latch, which is received within a keep when the lock is activated. When the lock is deactivated the locking member can be withdrawn from the keep. A lock mechanism is typically used to selectively restrict or control movement of a lock and/or control the locking member.
Lockable enclosures are used in many indoor or outdoor environments, both commercial and residential, to restrict access to various items by providing the enclosure with a lockable door, lid, drawer or other barrier. An example of such an enclosure is a key safe which is configured to securely house one or more keys and is affixed external to an entry door or building. The key safe comprises a locking mechanism, such as a pushbutton or combination dial locking mechanism, such that authorised users may enter the required unlocking combination or sequence and gain access to the one or more keys housed in the key safe. Additionally or alternatively, the lockable enclosure may house one or more credit and/or debit cards and/or money.
It is increasingly common for such key safes (or other locking enclosures) to comprise a mechanical pushbutton locking mechanism. Mechanical pushbutton locking mechanisms do not require an electrical power source to maintain accessibility to or function of the locking mechanism, thus there is no security risk posed by power outages or battery depletion.
Typically, a mechanical pushbutton lock comprises a series of buttons, each button configured to be disposed in either a depressed or selected position or an un-pressed or unselected position. When only the correct buttons have been pressed (irrelevant of the order in which the buttons are selected) the locking mechanism is configured to move a locking member from a locked position to an unlocked position. In practice, the security provided by these mechanisms may be inadequate, as the number of potential code combinations is limited because the codes are not sequence dependent. As such, the codes can be broken relatively quickly and easily by an unauthorised user simply by exhausting all of the possible code combinations.
A known solution to this problem is to use a mechanical pushbutton lock comprising a large number of buttons, thereby increasing the number of potential code combinations. This increases the security of the lock as it makes it more difficult for an unauthorised person to determine the correct code. However, in order to accommodate the additional buttons, the lock can be cumbersomely large. Also, if the code is too long it is easy for an authorised person to forget it, preventing them from opening the enclosure.
An alternative known solution is to use a mechanical pushbutton lock, wherein each button can be pressed multiple times (e.g. two or more times), sometimes known as a multi-press mechanical pushbutton lock. This increases the number of potential code combinations without increasing the number of buttons required on the locking mechanism. An example of a multi-press mechanical pushbutton lock is disclosed in US 2011/0132049.
In certain circumstances, it may be possible to break (also known as pick) a mechanical pushbutton lock, both the standard and multi-press version, without systematically trying each possible code combination. For example, and in broad terms, a skilled lock-breaker can turn the lever or other actuator to open the enclosure and then press the buttons until he hears and/or feels the locking mechanism click into the unlocked position.